Keeping Track of Change

Have you ever wanted to turn back time after making a mistake and irrevocably damaging a file you were editing? You can do so with minimal effort after reading this article.

For years, software developers have been
keeping track of all their changes to programs they are developing
with what they call “version control” software. However, even
competent developers have sometimes found it too troublesome to use
these tools except where they find it absolutely necessary, and so
it is not surprising that very few non-developers have used these
tools at all.

The reason that they find these tools so difficult to use is
that the rules for how to use them are written with the
most complicated situations in mind. For most personal
use of these tools, that is like learning to fly a jet aircraft in
order to drive a car. There is an easier way.

The assumption that makes everyone do so much extra work is
that more than one person will be trying to modify the
file at the same time. For your own personal files, or
for keeping track of changes to system files when you are the only
system administrator, that is not an issue.

The standard program for doing version control under Linux
(and most other versions of Unix) is GNU's
RCS, which stands for
Revision
Control
System. It has many options, but
you hardly need to know about any of them to make good use of it.
You can treat RCS as one of the simplest tools on your
system.

In fact, you can keep track of all the changes that you ever
make to a file with one command. Run the command ci -l
filename each time you make a
change to the file (“ci” stands for
“check
in”; you are “checking in your
changes”). The first time you do this, you will be given the
option to describe the file:

$ ci -l foofoo,v <-- foo
enter description, terminated with single '.'
or end of file:
NOTE: This is NOT the log message!
>

You are not required to describe the file, but you can if you
like. Then type a .
character on its own line, or press ^D on an
empty line.

When you have made a change to the file, you need type only
one command to tell RCS to keep track of that change for
you:

Here, you may wish to describe the change you have just made,
especially if you think you will want to examine the change at some
future time, but it is not required.

Remembering that single command is enough to prepare you for
disaster. The rest of this short article will show you a few easy
tricks that make RCS a little more comfortable
to use, and help you learn how to recover from disaster.

Even Easier?

If you think running one command each time you finish editing
a file is still too much work, we can make it
even easier for you! (Laziness is a virtue if
it causes you to work smarter instead of harder.)

We'll use a shell script. You can create
a file in your own “bin” directory (if your account is on a
computer shared with other people) or in /usr/local/bin (if you are
using your own computer). Whichever directory you choose must be
listed in your PATH. To make it easy to type,
we'll call it et, short for edit
text.

Type that into a file named
et, without making any typos. Then
run the command chmod +x et to make the file
executable. Now, you will be able to run
et filename to edit
and then automatically check in your changes.

The #!/bin/bash line tells Linux this
script is a shell script that is interpreted by the bash shell,
which comes as a standard part of every Linux distribution. All the
other lines starting with a # character are
comments, and are ignored by bash.

If you decide that you will never want to include a
description of the changes you have made, you can change the last
line of the script to

[ -f $1 ] && echo "." | ci -l $1

The reason for the [ -f $1 ] part is so
that if you type et
mistake, and then quit the
editor without saving the file, you won't get error messages when
ci finds that there is no file for it to check in.

The ${EDITOR-vi} part runs your favorite
editor, or if you have not chosen a favorite editor, it defaults to
the old standard vi editor. You can choose a default other than vi;
pico, jed, joe, Emacs, and other editors are all possibilities. For
example:

${EDITOR-jed} $1

will run jed, unless you have chosen some other favorite
editor.

To choose your favorite editor, which will apply to all
programs that want you to choose an editor, not just
et, you will need to set the
EDITOR environment variable to the name of the
editor you want to use. If you are using a bourne shell, such as
bash, zsh, pdksh, ksh, or sh, you will want to add a line like the
following to the file .profile in your home directory:

EDITOR=jed ; export EDITOR

If you use the C shell (csh or tcsh), you will want to add a
line like the following to the file .login in your home
directory:

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